Field of the Disclosure
The present disclosure relates generally to medical devices, more specifically spinal rods for immobilizing and stabilizing vertebral bodies of the spine.
Background
The spine is formed of a column of vertebra that extends between the cranium and pelvis. The three major sections of the spine are known as the cervical, thoracic and lumbar regions. There are 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae, with each of the 24 vertebrae being separated from each other by an intervertebral disc. A series of about 9 fused vertebrae extend from the lumbar region of the spine and make up the pelvic region of the vertebral column. These fused vertebrae consist of the sacral and coccygeal region of the vertebral column.
The main functions of the spine are to provide support and protect the spinal cord. Even slight disruptions to either the intervertebral discs or vertebrae can result in serious discomfort due to decompression of nerve fibers either within the spinal cord or extending from the spinal cord. If a disruption to the spine becomes severe enough, damage to a nerve or part of the spinal cord may occur and can result in partial to total loss of bodily functions (e.g. walking, talking, and breathing).
Each year millions of people suffer from back pain arising from defects in the intervertebral disc space. Commonly, surgical interventions directed at promoting fusion across the affected joint are employed to permanently provide long term pain relief to the patient. Typically, such fusion surgeries involve performing a partial or complete discectomy to prepare the disc space, and then implanting a natural or synthetic intervertebral fusion implant within the prepared disc space.
Surgical procedures on the spine (for example, procedures meant to fuse two or more vertebra together) often include the immobilization of two or more vertebra. Immobilizing the vertebrae may be accomplished in many ways (e.g. fixation plates and pedicle screw systems). One of the most common methods for achieving the desired immobilization is through the application of bone anchors (most often introduced into the pedicles associated with the respective vertebra to be fixed) that are then connected by rigid rods locked to each pedicle screw. Pedicle screws generally include an anchor component and a rod-housing component (or “tulip”) that is often coupled to the anchor component in a manner that permits angular adjustability of the tulip relative to the anchor component in one or more planes. Once the pedicle screws are implanted in the desired positions a spinal rod is seated in each tulip and locked in position.
One complication of spinal surgery is failure of the implanted components. Rod failure can occur where rod strength is compromised during bending of the rods to fit patient anatomy, or where the stress loads placed on the rod are too great. Therefore, in some procedures that are known to introduce higher stress to the implanted rod, such as pedicle subtraction osteotomy (PSO), it may be desirable to provide increased strength to the rod to increase stability and support to prevent negative outcomes that can result from rod failure.
It is desirable that an improved rod increase the stiffness and fatigue strength of the construct while having a minimal effect on the ease with which the construct is implanted and/or the amount of hardware needed to enhance the strength of the construct (e.g. in comparison to current techniques employing multiple side-by-side rods connected by a series of connectors). An improved rod as disclosed herein could be used for increased stability of short or long constructs, trauma, or posterior reconstruction, in support of spinal fusion. For example, the improved rod disclosed herein may help reduce the incidence of rod fracture across a PSO or unstable construct.